This invention relates generally to mechanisms for mixing a powder with a liquid to form a homogeneous paste, and more particularly to a high-speed, fully automatic apparatus for this purpose in which the liquid and powder are intermixed within a chamber from which air is withdrawn to control the entrainment of air in the paste.
While the invention will be described in connection with the production of dough for making bakery products such as bread, pizza and pastry, it is to be understood that the mixing mechanism included in the apparatus has many other practical applications unrelated to bakery products.
From the standpoint of production volume, bread is the most important baked product. Mixing is the first active step in bread production. The ingredients involved in mixing are flour and a dough-forming solution constituted typically by water, yeast, sugar, salt, milk and shortening. Ideally, mixing should result in a uniform mixture forming a smooth dough; it should develop the gluten in the dough in order to promote the elasticity of the dough and permit it to retain the gases generated by the yeast; and it should distribute the yeast cells uniformly so that they will receive proper nutrition.
The fact that dough can be rapidly produced has been confirmed by Bernadin et al. in their article "Hydrated Protein Fibrils from Wheat Endosperm" in the periodical Cereal Chemistry--September--October 1968, Vol. 50, No. 5. This article points out that flour hydration occurs very rapidly; for wetting a single particle of flour in a droplet of water requires less than 0.05 sec. for complete hydration, a hydrated protein web spreading quickly from the particle. Adjacent flour particles spreading similar protein networks interact to form a continuous system that can be worked mechanically to form a dough-like mass.
In traditional techniques for producing dough, such as the batch method which uses heavy blades revolving in a large bowl to mix the flour and dough-forming solution into a homogeneous mass, a number of steps must be separately performed which render the process time-consuming and costly. Moreover, the resultant dough is not entirely homogeneous, giving rise to non-uniform dough balls and a final baked product of unpredictable consistency.
In my prior U.S. Pat. No. 3,888,997, entitled "Method and Apparatus for Processing Dough," there is disclosed a mechanism operating at exceptionally high speed to effect continuous mixing, all necessary steps being carried out automatically from the initial step of feeding the flour and the dough-forming solution into the machine to the final step of forming divided units of the processed dough ready for baking. This patented mechanism obviates many of the drawbacks experienced with conventional techniques. In my prior patent, a screw rotating within a vertical tubular chamber acts to centrifugally hurl flour fed into the chamber against the inner wall thereof, thereby depositing a thin film of flour on the inner wall. Also fed into the chamber is the dough-forming solution which admixes with the thin film of flour to form on the inner wall a pasty film which is directed downwardly along a helical path. The pasty film is scraped from the inner wall to produce a downwardly-extending ribbon that is subjected to a kneading action.
The flour fed into the mixing chamber is introduced therein through a hopper having an outlet of fixed dimensions. The practical difficulty with this fixed feed arrangement is that it fails to take into account the changing flowability of flour with variations in ambient temperature and humidity. It also does not accommodate the feed to the disparate characteristics of various flours. One, therefore, is not always able to attain optimum flour flow conditions.
Flour, which is a finely ground meal of wheat, is the backbone and structure of baked goods, flour acting both as a binding and absorbing agent. Wheat is the only cereal that contains the proper combination of glutenin and gliaden for bread-making. When combined with water, these constituents form gluten which is essential for retaining the gas produced by yeast.
However, the form of wheat used depends on the ultimate product. Thus there are several kinds of so-called hard wheat, the choice depending on the final product (i.e., rolls or bread). Cakes and cookies are derived from various types of soft wheat. In some instances, rye flour milled from rye grain may be blended into wheat flour.
The need exists, therefore, for means to adjust the feed of flour in an arrangement of the type disclosed in my prior patent to accommodate the machine to changing ambient conditions and to different flour characteristics. In my copending application, means are provided to adjust the input feed of flour so that the rate of feed takes into account the characteristics of the flour and the prevailing ambient conditions.
In my prior patent and in my copending application, the dough-producing solution is admitted through a channel cut in the shaft on which the main screw is mounted. This channel communicates with nozzles formed in the rotating screw from which the solution is ejected against the thin film of flour to admix therewith, thereby forming a paste that is thereafter developed by a screw action to produce dough.
The present invention is limited to the mixing of powder such as flour and a liquid, the subsequent steps of development, proofing, etc., not being the concern of the present invention.
When the liquid is introduced in the manner disclosed in my prior patent and copending application and is hurled centrifugally against a thin film of flour, this turbulent jet action tends to entrain air in the resultant paste.
While the existence of some air bubbles in the paste does not adversely affect the quality of the dough produced from the paste, an excessive amount of such bubbles may be undesirable in some instances.
Thus in the making of dough by the conventional batch process, the present practice includes the use of degassers which roll or otherwise manipulates the dough to squeeze out large air bubbles therefrom. And in order to produce a so-called "strong" or coherent dough that will not separate when handled, it is also the common practice to add oxidizing agents therein such as potassium bromide or ascorbic acid.
While it is desirable, depending on the end product, to have minute air bubbles well dispersed throughout the dough, the existence of large bubbles therein is usually objectionable. There is no optimum dispersion of air bubbles that is applicable to all doughs, for the bubble requirements depend on the ultimate products; hence some degree of or control or flexibility is required in producing a paste from which the dough is to be made.